Characterization of clonogenic cells in refractory anemia with excess of blasts (RAEB-CFU): response to recombinant hematopoietic growth factors and maturation phenotypes.

The proliferative and maturation abilities of bone marrow progenitors in patients with refractory anemia with excess of blasts (RAEB) and RAEB in transformation (RAEB-T) have previously been investigated in vitro using impure sources of colony stimulating activity. Here we report studies that were concerned with defining growth factor responses of RAEB progenitors (RAEB-CFU) in colony culture using pure hematopoietic growth factors. Marrow cells of 10 RAEB patients were cultured with recombinant IL3, GM-CSF, G-CSF, M-CSF and EPO. Factor dependent colony growth of four patients was examined in detail cytologically. The analysis revealed notable deficiencies in the colony forming spectrum as compared with normal marrow: although granulocytic colonies were formed in all of these four RAEB cases, macrophage colonies could not be induced in 1/4 cases and eosinophilic and erythroid colony formation could not be propagated in 2/4 cases with the proper stimuli. These findings are indicative of the intrinsic incapabilities of RAEB-CFU to mature along certain differentiation pathways in response to the growth factors. We then determined the surface phenotypes of RAEB-CFU using MoAbs Vim-2 (myelomonocytic) and B13C5 (CD34) following dual labeling and fluorescence activated cell sorting and subsequent culture of the separately sorted BI3C5+/Vim-2+, BIC5+/Vim-2-, BI3C5-/Vim-2+ and BIC5-/Vim-2- cells. In normal marrow most clonogenic cells were recovered from the BI3C5+/Vim-2- fraction. In contrast, in RAEB marrow increased proportions of the colony forming cells were BI3C5+/Vim-2+, BI3C5-/Vim-2+, or BI3C5-. The altered distribution of surface immunophenotypes of RAEB-CFU provides further evidence for the imbalance of maturation in the progenitor cell compartment. The results are discussed in view of the concept that the inabilities of the RAEB hematopoietic precursors to mature in response to the hematopoietic growth factors are partial and variable, but may culminate in a progressive loss of the differentiation competence of the progenitors when leukemia evolves.